One-group posttest-only design

why one-group posttest-only design is not useful

no pretest and no control group, w/out a pretest, it is diff to know if the treatment effect produced a change, almost all threats to internal validity apply (useful only when specific background info exists)

Strong designs

control group

group that does NOT get the IV or gets some standard value--responses of this group must stand for responses that particpants in teh experimental group would have given if they did not receive the treatment condition

within participants design

type of within participants design

posttest-only control-group design

participants randomly assigned to a treatment condition; the DV is measured only once after treatment condition is administered to the experimental gorup--then responses of experimental group compared to the responses of the control group

pretest-posttest control group design steps:

1. participants are randomly assigned to groups and then pretested on the DV
2. the IV is then administered to the experimental group
3. the experimental and control groups are posttested on the DV
4. diffs btwn pre and post test scores for experimental vs. control group then statistically tested to assess effect of IV

main function of the pretest

reason for a pretest design

1. to determine if randomization worked
2. ANCOVA (anal of covariance) to control for any pretest diffs
3. increase sensititvity
4. test for ceiling effect
to test for initial position of participants on the DV
5. to obtain evidence of change

drawbacks to pretesting

why is sensitization of participants to treatment condition most serious prob?

1.participants knowledge could heighten their sensitivity to the IV
2. participants responses may produce responses that are NOT representative of those that would have been obtained if pretest not occured
3.results might not generalize to other participants who have not taken pretest
4. effet of pretesting is dependent on the type of study conducted

within-participants posttest-only design

advantages of within-participants design

equiv of research participants 100% bc they are the same participants involved in each treatment condtion (so participants serve as their own control, variables remain constant over entire experiment, and increases sensitivity of experiment-maximally sensitive to the effects of the IV) & requires fewer participants than BTWN-participants design

Factorial design

how are factorial designs made?

1. participants randomly assigned to groups
2. a factorial design is described in terms of the number of independent variables it uses and the # of conditions or levels of each IV
3. a 2x2 design has 2 IVs each w/ 2 conditions
4. a 3x3 design has 3 IVs two of which has 3 levels and one that has 2 levels

disadvantages of factorial designs

advantages of factorial designs

1. can manip more than one IV, which allows us to test multiple/more precise hypoth at once
2. can control potential confounding extraneous variable by building it into the design (gender)
3. provides greater precision when you add mor than one IV
4. can test the effect of interactions, which can give us a better understanding of the given phenomenon